This invention concerns a process and reactor for the preparation of polytrimethylene ether glycol from 1,3-propanediol reactant. In addition, the invention is directed to a continuous multi-stage process in an up-flow column reactor involving forming a gas or vapor phase by-product.
Known polyalkylene ether glycols include polyethylene glycol, poly-1,2-and 1,3-propylene ether glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol and copolymers thereof. They have been used widely as lubricants or as starting materials for preparing lubricants used in the molding of rubbers and in the treatment of fibers, ceramics and metals. They have also been used as starting materials for preparing cosmetics and medicines, as starting materials or additives for water-based paints, paper coatings, adhesives, cellophane, printing inks, abrasives and surfactants and as starting materials for preparing resins, such as alkyd resins. They have also been used as soft, flexible segments in the preparation of copolymers and segmented copolymers such as polyurethanes, thermoplastic polyesters and unsaturated polyester resins. Examples of commercially important polyether glycols include polyethylene glycol, poly(1,2-propylene glycol), ethylene oxide/propylene oxide copolyols, and polytetramethylene ether glycol.
Among the polyether glycols, the most widely used polyether glycol is poly(1,2-propylene glycol) (PPG) because of its low cost. This polymer is non-crystalline, liquid at room temperature and hence easy to handle. However, PPG has secondary hydroxyl end groups and it contains high percentages of terminal unsaturation.
Polyoxytrimethylene glycol or polytrimethylene ether glycol or poly(1,3-propylene glycol) can be derived either from 1,3-propanediol or from oxetane. These polytrimethylene ether glycols have primary hydroxyl groups and have low melting points and are highly flexible.
U.S. Pat. No. 2,520,733, which is incorporated herein by reference, discloses polymers and copolymers of trimethylene glycol and a process for the preparation of these polymers from trimethylene glycol in the presence of a dehydration catalyst such as iodine, inorganic acids (e.g., sulfuric acid) and organic acids. The trimethylene glycol derived polymers disclosed in this patent are dark brown or black in color. The color can be improved to a light yellow color by treatment processes disclosed therein. Polymers of molecular weight from about 100 to about 10,000 are mentioned; however, there is a preference for molecular weights of 200-1,500 and the highest molecular weight shown in the examples is 1096.
U.S. Pat. No. 3,326,985, which is incorporated herein by reference, discloses a process for forming a polytrimethylene glycol having an average molecular weight of 1,200-1,400. First, polytrimethylene glycol which has an average molecular weight of about 900 is formed using hydriodic acid. This is followed by an after treatment which comprises vacuum stripping the polyglycol at a temperature in the range of 220-240xc2x0 C. and at a pressure of 1-8 mm Hg in a current of nitrogen from 1-6 hours. The product is stated to be useful in preparing polyurethane elastomers. There is also presented a comparative example directed to producing polytrimethylene glycol with a molecular weight of 1,500.
U.S. Pat. No. 5,403,912, which is incorporated herein by reference, disclosed a process for the polymerization of polyhydroxy compounds, including alkanediols having from 2-20 carbon atoms, in the presence of an acid resin catalyst at temperatures of from 130-220xc2x0 C. Molecular weights of from 150 to 10,000 are mentioned. A copolymer of 1,10-decanediol and 1,3-propanediol having a number average molecular weight of 2050 was exemplified.
Preparation of ester terminated polyethers and hydroxy terminated polyethers from oxetanes and or mixtures of oxetanes and oxolanes by ring opening polymerization is disclosed U.S. Pat. No. 4,970,295, which is incorporated herein by reference. The resulting polyethers are stated to have molecular weights in the range of 250-10,000, preferably 500-4,000. Synthesis of polyoxytrimethylene glycols from oxetane is also described in S.V. Conjeevaram, et al., Journal of Polymer Science: Polymer Chemistry Ed., Vol. 23, pp 429-44 (1985), which is incorporated herein by reference.
It is desirable to prepare said polyether glycol from readily available materials, not, for example, from the commercially unavailable oxetane. The polytrimethylene ether glycols heretofore obtained from the polycondensation of 1,3-propanediol are of low molecular weight, are highly discolored and/or require long reaction times. In addition, heretofore all process for preparing polytrimethylene ether glycol from 1,3-propanediol reactant have been batch processes. Therefore, a continuous process that produces polytrimethylene ether glycol in high yield, preferably with little or no color, and desired molecular weight, has been sought.
This invention is directed to a process of making polytrimethylene ether glycol comprising:
(a) providing 1,3-propanediol reactant and polycondensation catalyst; and
(b) continuously polycondensing the 1,3-propanediol reactant to polytrimethylene ether glycol.
Preferably, the polycondensing is carried out in two or more reaction stages.
The polycondensing is preferably carried out at a temperature greater than 150xc2x0 C., more preferably greater than 160xc2x0 C., and most preferably greater than 180xc2x0 C., and is preferably carried out at a temperature less than 250xc2x0 C., more preferably less than 220xc2x0 C., and most preferably less than 210xc2x0 C.
The polycondensation is preferably carried out at a pressure of less than one atmosphere, more preferably less than 500 mm Hg, and even more preferably less than 250 mm Hg. While still lower pressures, for example, even as low as 1 mm Hg can be used, especially for small scale operation, for larger scale, pressure is at least 20 mm Hg, preferably at least 50 mm Hg. On a commercial scale, the polycondensation pressure will normally be between 50 and 250 mm Hg.
In one preferred embodiment, the 1,3-propanediol reactant is selected from the group consisting of 1,3-propanediol and/or dimer and trimer of 1,3-propanediol and mixtures thereof. In another preferred embodiment, the 1,3-propanediol reactant is selected from the group consisting of the 1,3-propanediol or the mixture containing at least 90 weight % of 1,3-propanediol. In yet another preferred embodiment, the 1,3-propanediol reactant is the 1,3-propanediol.
In one preferred embodiment, the catalyst is homogeneous. Preferably, the catalyst is selected from the group consisting of a Lewis Acid, a Bronsted Acid, a super acid, and mixtures thereof. More preferably, the catalyst is selected from the group consisting of inorganic acids, organic sulfonic acids, heteropolyacids, and metal salts thereof. Even more preferably the catalyst is selected from the group consisting of sulfuric acid, fluorosulfonic acid, phosphorus acid, p-toluenesulfonic acid, benzenesulfonic acid, phosphotungstic acid, phosphomolybdic acid, trifluoromethanesulfonic acid, 1,1,2,2-tetrafluoro-ethanesulfonic acid, 1,1,1,2,3,3-hexafluoropropanesulfonic acid, bismuth triflate, yttrium triflate, ytterbium triflate, neodymium triflate, lanthanum triflate, scandium triflate and zirconium triflate. The most preferred catalyst is sulfuric acid.
In another preferred embodiment, the catalyst is heterogeneous. Preferably, the catalyst is selected from the group consisting of zeolites, fluorinated alumina, acid-treated silica, acid-treated silica-alumina, heteropolyacids and heteropolyacids supported on zirconia, titania, alumina and/or silica.
In a preferred embodiment, the polycondensation is carried out in a reactor equipped with a heat source located within the reaction medium.
In one preferred embodiment, the polycondensation is carried out in an up-flow co-current column reactor and the 1,3-propanediol reactant and polytrimethylene ether glycol flow upward co-currently with the flow of gases and vapors. Preferably, the reactor has two or more stages, more preferably 3-30 stages, even more preferably 4-20 stages, and most preferably 8-15 stages.
In one preferred embodiment, the 1,3-propanediol reactant is fed at multiple locations to the reactor. In addition, an inert gas is preferably added to the reactor at one or more stages. Further, preferably at least some amount of steam (water vapor) that is generated as a by-product of the reaction is removed from the reactor at least one intermediate stage.
In another preferred embodiment, the polycondensation is carried out in a counter current vertical reactor wherein and the 1,3-propanediol reactant and polytrimethylene ether glycol flow in a manner counter-current to the flow of gases and vapors. Preferably, the reactor has two or more stages, more preferably 3-30 stages, even more preferably 4-20 stages, and most preferably 8-15 stages. Preferably, the 1,3-propanediol reactant is fed at the top of the reactor. Even more preferably, the 1,3-propanediol reactant is fed at multiple locations to the reactor.
In yet another preferred embodiment, the polycondensation is first carried out in at least one prepolymerizer reactor and then continued in a column reactor. The 1,3-propanediol reactant preferably comprises 90 weight % or more 1,3-propanediol. Preferably, in the prepolymerizer reactor the 1,3-propanediol is polymerized with the catalyst to a degree of polymerization of at least 5. More preferably, the 1,3-propanediol is polymerized with the catalyst to a degree of polymerization of at least 10 and the column reactor comprises 3-30 stages. Preferably, in the at least one prepolymerizer reactor the 1,3-propanediol is polymerized with the catalyst to a degree of polymerization of at least 20. In the most preferred embodiment, the at least one prepolymerizer reactor the 1,3-propanediol is polymerized with the catalyst to a degree of polymerization of 5-10. Most preferably, the at least one prepolymerizer reactor is a well-mixed tank reactor. Most preferably, steam generated in the at least one prepolymerizer reactor is removed and the product of the at least one prepolymerizer is fed to the column reactor.
Preferably, an inert gas is fed to the column reactor.
This invention is also directed to a continuous multi-stage process comprising reacting at least one reactant in a liquid phase in an up-flow column reactor, and forming a gas or vapor phase by-product wherein the gas or vapor phase by-product is continuously removed at the top and at least one intermediate stage. Preferably, the gas or vapor phase by-product is water.